“To prune or not to prune,” is the most often asked question. It should be noted that incorrect pruning will never bring an early death to the clematis.
At worst an inappropriate pruning will only delay flowering. Furthermore, if all varieties were left unpruned they would all flower very well. However, as is explained below, the flowers would not necessarily cover the plant as well as they otherwise could.
Our first tip on pruning applies to all clematis varieties. The first February or March after planting all clematis should be cut back. At this time, you should be able to see leaf buds developing as your plant breaks dormancy. You should leave two sets of buds on each stem between where you make your cut and soil level. In subsequent years the following recommendations should be used.
In an effort to simplify things, we have used three main pruning categories.
Group (A) are varieties that flower only on growth produced the previous year. Pruning should consist of cutting out weak or dead stems as soon as they are finished blooming in May or June. Pruning later than June or very severe pruning will result in fewer blooms the following spring. The very popular montana varieties fall into this group and even though they will survive in our colder climates, if the tops are nipped off by extreme frosts, blooms that should have occurred in early spring might occur in the fall, if at all.
Group (B) Group B is broken down into two sub groups:
Group (B) (1) are the varieties that flower on wood that has been hardened by the previous season’s growth. Normal blooming patterns for this group consist of a heavy flush of flowers in May – June on the previous season’s growth followed by a second smaller flush of blooms in September on the current season’s growth.
Group B (2) are the varieties that bloom simultaneously on last year’s growth and the current season’s growth. Group B (2) varieties normally bloom from June to September continuously. For pruning purposes these varieties can be treated either as group B (1) or group C and for that reason work extremely well in combination plantings with group B (1) or group C varieties. If planted alone a group C pruning regime every second year is recommended.
For both group B (1) and B (2), in late February or March a light pruning with some variation in the length of the stems will help produce a well balanced group B plant. Any weak or dead wood should be removed at this time and a careful spacing of the remaining stems is all that is required. The spacing of the stems will allow room for next springs mass of blooms to open pleasingly. A severe pruning will reduce the number of blooms at the plant’s next flowering, but will not hurt the plant; in many cases it will help produce a better balanced plant. If your group B clematis has been neglected for many years, it can be rejuvenated by severely cutting back most of the old growth. It is always amazing how quickly new growth appears. Separate and direct the new shoots or they will soon grow skyward in a tangled mess.
Group (C) These varieties bloom only on the current year’s growth. Blooms commence in early summer and continue through to fall. Plants should be cut back in late February or March to two strong sets of buds on each stem as close to ground level as possible. This will provide a plant with blooms that start near ground level and continue to the top of the plant. The majority of the group C clematis start their new growth very close to where last season’s growth ended; so if left unpruned they will very quickly grow out of control. If you want to grow a group C clematis through a tree or have it bloom in an area above its normal blooming height, this characteristic can be used to your advantage. You can prune an established plant at almost any height or not prune at all to accomplish your objective. Keep in mind that group C clematis bloom on the current season’s growth, so that if treated in an untraditional way the blooms will be at the top of the plant and a bare stem will gradually appear over a few years. This provides an opportunity to plant a lower growing group B variety to hide the bare stem and to extend the blooming season.